Survival and development of dopaminergic neurons from embryonic rat mesencephalon were examined in dissociated cell cultures. Survival and the degree of development were assessed by measuring the amount of labelled dopamine taken up by the high affinity dopamine reuptake system. The development of this system correlates well with the development of the dopaminergic neurons. Soluble factors in the culture medium play a dominant role in the survival, development and subsequent maintenance of these cells in vitro. Removal of these factors from young cultures (one week in vitro) appears to disrupt all the cells in culture. Removal from more mature cultures (two weeks or more in vitro) did not cause obvious morphologic damage but did cause the rapid inactivation or loss of the dopamine reuptake system. The more developed dopaminergic neurons apparently depend on soluble factors for continued survival or to maintain a functioning reuptake system.